1984546 MuSK MG Muscle-specific tyrosine kinase myasthenia gravis 2 1984542 MuSK MG MuSK antibody-mediated MG 2 1984543 MuSK MG anti-muscle specific kinase antibody-positive MG 1 1984545 MuSK MG Muscle-specific kinase myasthenia gravis 1 1984544 MuSK MG muscle-specific tyrosine kinase Ab-positive MG 1